Final Assessment: Honshu's Rivers and Their Fate.

The island of Honshu boasts some of the fastest flowing rivers in the world. This is due to the steep gradients of the mountains, the tight snowpack on their peaks, the impermeability of these mountains attributing to higher amounts of runoff from melting snow and rainfall, and the rivers flowing radially from the peaks to the ocean(1). These factors, along with the high volumes of water wearing away at the mountains, have helped in creating many of the v-shaped valleys and alluvial plains that surround Honshu.

Drainage from Mt. Fuji helps in the speed and volume of the rivers of Honshu (1)

Chomonkyo Gorge (Southwestern Honshu) created by the rivers of Honshu (2)

Honshu 1000 Years From Now

Because of the high speeds and amounts of water flowing from the mountains of Honshu, I theorize that, barring dramatic climate change, these rivers will eventually begin to wear down the river bed and set the table for becoming more graded streams. Already, in the present day, these rivers do not have many factors working against them. They have very steep slopes and smoother surfaces then most rivers, based on the speed of their flow. As the river begins to wear down the mountain, we will see a gradual increase in erosion of the knickpoints in the river. In 1000 years, waterfalls such as the Shomyo Waterfall will be less pronounced then it is now and shows signs of knickpoint erosion in the present. Undercutting to some degree is also occurring near the base (located next to it, Hannoki Waterfall is not a permanent waterfall; it depends heavily on snowpack, but it, too, is showing signs of erosion) (2). In 1000 years this and other waterfalls in Honshu will have less discharge and look less like a waterfall. Deposition will begin to take place when the river floods.  

Shomyo Fall (left side) with several knickpoints just below the mouth and right before flowing into the river (3)

Akiu Falls (Northern Honshu) showing possible signs of an eroding  bed at two locations (4)

Bandokoro Waterfall (Central Honshu ) showing several erodable knickpoints and possibly an undercut (5)

Honshu 10,000 Years From Now

In 10,000 years, my hypothesis (maintaining weather and climate as providing enough precipitation) is that the rivers will have most likely either reached equilibrium or simply require a few thousand more years. Evidence of waterfalls will be minuscule. As erosion takes place, these newly designed rivers begin to meet less steep gradients-as they still come down very steep mountains-and they deposit the sediments they acquired at the foot of the mountains, creating alluvial fans (3). They should share similar characteristics of the alluvial fan at the foot of the Himalayas, sized at 58,000 miles, created from the Koshi River as it comes down the Himalaya Mountains (3).

10,000 years from now, many of the alluvial fans in Honshu should have similar characteristics of the Koshi River alluvial fan (above) (6)

 Honshu 1,000,000 Years From Now

By this point, the rivers left in Honshu will have finally reached that desired equilibrium. Rivers have degraded many times over by this point. Due to the volume of sediment deposited, energy expended in depositing, and that many of Honshu's rivers are higher order rivers, many of them will erode and become canyons (4). Evidence of terraces will be observed (5). Many of Honshu's rivers are mere shadows of their former self.

Conclusion

These processes together, banking that precipitation is sufficient, are capable of transforming Honshu's landscape entirely. In seeking equilibrium, the rivers need to expend large amounts of energy. This, coupled with how much needs to be eroded and deposited, will make Honshu a land of canyons and meandering rivers, and make their fast paced rivers a thing of the past. 

The basic process of what Honshu could possibly look like 1,000,000 years in the future. (7)

Picture Source

1.  http://i.ytimg.com/vi/twF-puBoARc/0.jpg

2. http://upload.wikimedia.org/wikipedia/commons/a/a6/Chomonkyo_2.jpg

3. http://www.world-of-waterfalls.com/asia-shomyo-waterfall.html

4. http://www.world-of-waterfalls.com/asia-akiu-waterfall.html

5. http://www.world-of-waterfalls.com/asia-bandokoro-waterfall.html

6. http://www.nicholas.duke.edu/eos/geo41/str052.gif

7. http://library.thinkquest.org/C005280/geoformation.htm

Work Cited

1. http://factsanddetails.com/japan.php?itemid=860&catid=26&subcatid=160

2. http://www.world-of-waterfalls.com/asia-shomyo-waterfall.html

3. http://education.nationalgeographic.com/education/encyclopedia/alluvial-fan/?ar_a=1

4. http://library.thinkquest.org/C005280/geoformation.htm

5. http://clasfaculty.ucdenver.edu/callen/1202/Landscapes/Fluvial/Fluvial.html